A steam turbine is a rotating machine intended to convert the thermal energy of steam into mechanical energy for driving an alternator, a pump or any other rotary mechanical receiver. In most cases the turbine includes a high-pressure module, possibly a medium-pressure module, and a low-pressure module. Steam supplied by a steam generator is fed to the high-pressure module and then to the medium-pressure and low-pressure modules.
The medium-pressure and low-pressure modules generally comprise a symmetrical or non-symmetrical single or double flow internal body enclosing a rotor equipped with mobile blades and supporting fixed vanes. The fixed vanes are constituted by a succession of deflectors suspended in said internal body and interleaved between the mobile stages of the rotor, said deflectors being adapted to guide the flow of steam in a specific direction toward the mobile blades of the rotor, accelerating the steam. A deflector typically includes an internal ring and an external ring connected to each by a multiplicity of identical vanes.
In some prior art fabrication methods each of the deflectors is welded manually to the internal ring and to the external ring. To execute these welds under the best conditions, the two ends of each vane intended to be welded to the internal and external rings of the deflector are chamfered by an operator so as to produce a filling space intended to accommodate a weld bead. This space, which can be likened to a peripheral groove formed around the vane, is delimited partly by the vane and by the corresponding ring and therefore allows the deposition of a greater quantity of welding material so as to reinforce the connection between said vane and said ring.
Now, until now, these chamfers have been produced manually by an operator using a grinding tool, the quality of said chamfers being therefore greatly dependent on the operator, as much at the level of their skills as their aptitude to carry out this grinding at the time. This results in a somewhat fluctuating quality of the chamfers, which can be harmful for the deflectors produced from such vanes. In fact, experience has shown that manual grinding of such chamfers remained somewhat approximate over a large quantity of vanes processed by this manual method and could reveal serious and harmful structural defects, such as cracks along the welded joints, for example. In order to remedy this situation, deemed unacceptable for the correct operation of the turbine, the risks of malfunction or accidents proving too high, the phase of machining the ends of each vane has been automated, by means of a machine designed to produce grooves of given shape and size, one after the other, repetitively, reliably and continuously. In this way, the fabrication method of the invention contributes to greatly reducing or even eliminating all risk of defects appearing in the deflector, linked to random machining of the vanes, and therefore to welded joints of smaller size and/or lesser quality.